Technology related to portable devices, specifically cellular telephones, is changing rapidly. Cellular telephones are becoming smaller, yet more powerful. One related technology that is rapidly changing along with the cellular telephone is battery technology and technology related to battery charging. Cellular telephone batteries are becoming smaller and more powerful, and there are multiple battery types that take advantage of different chemical formulations. One problem, however, related to these new generations of batteries is controlling the heat generated during charging, i.e., thermal control. During charging, a charger with a built-in pass transistor can become dangerously hot and the pass transistor can become damaged. In addition, if the heat is unregulated, the heat can damage internal parts of the cellular telephone or damage the battery itself. Fuel cells can rupture, completely destroying the battery, or the cellular telephone itself.
Several hardware approaches to thermal control have been attempted recently to regulate battery charging. These approaches are based on an integrated hardware control loop that regulates battery charging circuitry temperature during charging. One such approach is a 2-point hysteretic approach. In this approach, hardwired circuitry provides an upper temperature limit that is considered safe during charging, and if the upper temperature limit is reached, the charging process is either stopped or reduced to a lower charging rate until a lower temperature limit is reached. Once the lower temperature limit is reached, the charging rate returns to a normal level. This process repeats continuously, toggling back and forth dependent on the temperature of the charging circuitry.
Another approach is a hardwired thermal control loop providing continuous temperature feedback to a controller monitoring the charging circuitry temperature. This approach constantly measures the temperature of the charging circuitry, and adjusts charging power levels in a continuous-time analog or discrete time digital manner until a steady state temperature is reached.
A third approach involves a complete shutdown of the charging circuitry. Utilizing a temperature sensor, the temperature of the charging circuitry is monitored and if the temperature reaches a point above an acceptable temperature limit, the charging power is completely shut off until the charging circuitry temperature reaches a level at which it is considered safe to continue with charging. This approach, called a “duty-cycled power” approach, allows the charging current to be completely turned off for a percentage of the operating period and can also be combined with a decreased charging current approach to implement a flexible charging power scheme that effectively controls circuit heating.
These approaches all have drawbacks. Each approach involves hardwired circuitry, which provides less programmability, and thus results in a less flexible charging method. Due to the hardwiring, it is nearly impossible to build in flexible algorithms to monitor circuitry temperature and optimize battery charging currents and battery charging power.
What is needed is a software based temperature control for monitoring charging circuitry temperature and controlling charging rates to maintain an optimal temperature while still maintaining a high charging rate. Utilizing software control, the above mentioned problems, mainly lack of programmability and flexibility are resolved.